Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é a duração máxima do ensino secundário obrigatório?
 ###Tabelas: CREATE TABLE season_12:_2008_2009 (season_12:_2008_2009_id AUTO_INCREMENT PRIMARY KEY, Series Ep. VARCHAR, Episode INT, Netflix VARCHAR, Segment A VARCHAR, Segment B VARCHAR, Segment C VARCHAR, Segment D VARCHAR) CREATE TABLE cantonal_school_systems (cantonal_school_systems_id AUTO_INCREMENT PRIMARY KEY, Canton VARCHAR, Years of Kindergarten INT, Years of Kindergarten provided VARCHAR, Years of Kindergarten legally required VARCHAR, Length of Primary School INT, Length of mandatory Secondary School INT, Separate Secondary Schools? VARCHAR, Cooperative Secondary Schools? VARCHAR, Integrated Secondary Schools? VARCHAR) CREATE TABLE match_attendance (match_attendance_id AUTO_INCREMENT PRIMARY KEY, Team VARCHAR, Hosted INT, Average INT, Highest INT, Lowest INT, Total INT, Last Year INT, Up/Down VARCHAR) CREATE TABLE players_in_the_nba (players_in_the_nba_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, WSU Year(s) VARCHAR, Position VARCHAR, Team VARCHAR, Pro Year(s) VARCHAR) CREATE TABLE list_of_rmsp_company_vessels (list_of_rmsp_company_vessels_id AUTO_INCREMENT PRIMARY KEY, Ship VARCHAR, Date Commissioned INT, Gross Tonnage INT, Propulsion VARCHAR, Material VARCHAR)  
SELECT MAX Length of mandatory Secondary School FROM cantonal_school_systems